Process of reducing the corrosion of ferrous metals by ammoniacal solution and corrosion inhibitor therefor



a nitrogen solutions.

fiatenteci Oct. 7, 1952 ion-Iran YPMENT )OFFICE PROCESS OF REDUCING" 'LISHH EI' CORROSION I OF FERROUS METALS BY AMMONIACAL THEREFOR SOLUTION AND CO EROSION- mnnsrron Marion D} BarnesIBoyd L. Emhr y, and RussellE; KoonsyELDdradd, Ark., assignors to Lion Qil CompanmJiEli.Dorado, (Al ke; a corporationf of Delaware No Drawingf-Application Qctoher 2'7 195 0,

SerialNo. 192.628

lhe present invention relates to a process of reducing corrosion,. andmore particularly. to a I process 'of reducingfthe corrosion of ferlious .metals-by ammoniacalnsolutions ,of nitrogen commounds, known in the trade as'nitrogen solutions. One largeuselof nitrogen solutionsis} in the manufacture bfieritilizers. .The present,;.invention has particular. application inithe .,fer ti1lzer industry. Nitrogen compounds .involvedinthe ,manufacture. .of I fertilizers include ammonium nitrate, sodium. nitrate ahdnrea. ,Of j these, aminonium nitrate isperhaps Ithe. mostjimportant.

The corrosivene'sspf nitrogen solutions is a very serious problem...encountered in; theipflmahufaclturejldistribution. a'nduse. 1 The solutions very rapidlylcorrode ferrousmetal; e. g... mild steel, resu'ltin'g in a severe. metal loss,,an accumulation of a greenish-blackierrous sludge which gradually turns into arleddishebrown precipitatefoi ferricoXide; and a .severe cracking for the metal.

filh'us, equipment .usedtin theflmanfaoture, ship- I 'ping .and. storage of nitrogen solutions is nornially damagedbeyond.usewithin a few months L- orless. V Faced with this-serious situation, industry has spent. considerable timedand money in, research to -minimize' -the. problem. I The .corr'osiveness of .l nitrogensolutions .has. been lessened. by the additionvthereto onvarious;substancesv referred to in the. ar-t as corrosion. inhibitors.., Both .single inhibitors and combinations. of inhibitors have been employedl. i One possible, function of. .these -inl iib'itors is-to deposit a protective coating. on the-metal. with which .the .nitrogensolutions come i in contact and thereby :inhibit ordecrease the. corrosion oi .the. metal *by. the solutions. .Al-

though progress has been made in this regard,

7 the-problem has not been. solved satisfactorily. One chief disadvantage is that the corrosionrate,

although materially inhibited, is still-.undesira:

blyhighj A furtherdisadvantage is. that the inhibitors heretoforeused do notprevehtthenitroh gen solutions from becoming undesirably ,con-

taminated e. g., by suspended-corrosion products. An object of @this inventionis to provide-aproc:

- ess ofgreducing[corrosion of ferrous. -metal by A further. object is to provide a process otreducingthe.corrosion offerf-rous*meta1 bynitrogensolutions. whereby the corrosion is reduced to a point substantially be- 10W that provided for heretofore. .A still further object is to provide such a process which, is further characterized by maintaining the nitrogen solutions remarkably" clear. An additional object is to minimize the disadvantages 0f:the-pri0r 18, Claims, n.

r o ec s will ,be apparent from the description ofthis invention given hereinafter. A Iheaboveobjects are accomplished according ,to this invention bro adly by providing [and practicing. the-process which comprises incorporating in a. nitrogen solution a compound having an SH lgroupand an QI-lgroup; theamountbf the compoundbeing sufiicient' to substantially reduce ....the..rateiofcqrrosion oi aifer rous metal by'the 0 .s lut iend. cpi taetin Lil .SQh

. with, a .ierrous metal.

While improved results are realized by. incorporating alone the nitrogen. solution a com- 1 pound havi SH. .srqup. and an H gro p additional improved results to a. remarkable extent arepbtained by incorporating in addition to; said compound an inorganic trivalent arsenic compound.

QLSl-Igroup. a'ndan QI-l groupkeep the nitrogen so- ,The degreetowhich the compounds having an lution clear is surprisingly high. The remark- ,able, increaseinefiectiveness of these compounds ,Iin reducing the. corrosion when used together ,withjan inorganic trivalent arsenic compound is .stillmore surprising. The compounds having an .-,,SI -I.group. and an OH group used .alon proved to be relatively poor inhibitors .butexcellent in ,.maintaining the nitrogen solutionclear. These compounds in combination with an inorganic 30,

,t'rivalent arsenic compound improved. only very slightly, in their ability to impart olearness to the nitrogen solution, but the combination proved to, be. a farj, better inhibitor than inhibitors heretofore ,usedj and also. far. better, than would 3.5

b XDected, jud ing" from their effect when. used 3101 6. .,'I.hus itappearsthat either a synergistic effect of ,a high ordertakes. place or, new compoundformationtakes place.

a- Tnem e fO I PQli 1 hav n i H group and an OH group is comparatively small... 'EX- amples, of rsuch compounds include the .followins: -m rce tog ethan l. .ICH2SHCH2OH) 2.3-

dimercapto.."Qpropanol-l .ronzsncnsncnzon) l-mercapto propanol-Z (CHaCHOHCI-IzSH), 1- mercapto butanol-Z- .(CH3CH2CHOHCH2SH) 3- er o propanfl- H CH I L 1. vme ento ..-ph. v t o .ie nt liqlisezsm.

' .lem r tqfirmet y tunne -2 rmr n o prpnan i ziar (C'HZOI'ICHQHCHZSH) and isomers of said compounds... or these comr un z-mer p og .ethapelenq ,3edif r. er pto mally are not readily available commercially and are expensive to prepare.

The compounds containing H and SH groups may be prepared by any of the methods available in the chemical literature but more commonly by the treatment of epoxides with hydrogen sulring and the introductionof an OH group and SH group respectively on'the carbon atoms formerly joined through the oxygen atom of the epoxide ring. Alternatively compounds containfide which brings about rupture of the epoxide ing OH and SH groups may be prepared from compounds containing chlorine atoms and OH groups (e. g. chlorohydrins) by treating them with sodium sulfide, sodium hydrosulfide or other substance capable of yielding SH groups.

Inorganic trivalent arsenic compounds useful according to this invention include, e. g., sodium;

crease the solubility of the inorganic trivalent arsenic compound in the nitrogen solution, desirably such compound will be dissolved in an alkali such as dilute sodium hydroxide.

. In view of the foregoing and for the sake of clarity, thisinventionwill be described for the most part with referenceto'employing 2-mercapto ethanol and sodium arsenite in combination as a corrosion inhibitor for substantially retion of two inhibitors they were added separately to the ammonium nitrate solution, however they may be mixed prior to addition to-theammonium nitrate solution. The per cent sodium arsenite is calculated as arsenic trioxide (AS203). The results obtained are tabulated below:

. Pie'cenalnhtilb- Cari-051231 or ase mg. cm. ay Inhibitor the Nitrogen (Avg. for 30 Solution) days) Z-mercapto ethanol; 0. 157 Sodium arsenite 0. 175 Ammonium thiocyanate 0. l4 Butyi mercaptan. 0 r "0. l6 Z-mercapto ethanol and sodium 0.01 H arsenito. r

Ammonium thiocyanate and so- 0 19 dium arsenite. 0.05 Butyl mercaptan and sodium 0.1 oieach.. 0.13

arsenite. 2, 3-dimercapt0 propanol-l and 0.1 o 06 sodium arseulte. 0.05

ample is merely illustrative and does not limit the present invention, which more broadly comprises incorporating in a nitrogen solution a ducing the rate of corrosion of a ferrousmetal V by an ammoniacal ammonium nitrate solution, this being a preferred embodiment of the invention.

Ammoniacal ammonium nitrate solutions may vary-considerably in composition. Fairly representative of such solutions encountered in'industry and whichgive' rise to the corrosion problem discussedhereinbefore are those having approxi- -mately 50%-75T% ammonium nitrate,.15%-% ,free ammonia and the remainder mostly water. I

The quantity of inhibitor used is not critical over a fairly broad range and may vary upwards from a' very low percentage of th nitrogen solution. Below about 0.005% inhibitor by weight Example 354 parts of an ammoniacal ammonium nitrate solution, consisting of'66.8% ammonium nitrate and 16.6%anhydrous ammonia and 16.6% water,

was placed in a closed container. The inhibitor was added and a test specimen of mild steel suspended freely in the nitrogen solution. The test specimens were weighed daily throughout the as mg./cm. /day weight loss, 1

In this particular examplein'volving the addicompound having an SH group and an OH group, theamount of J said compound being sumcient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

In carrying out this invention according to a preferred embodiment thereof indicated hereinbefore, to a nitrogen solution in a railroad tank car (orstorage, conveying, measuring-and other handling equipment) are'added 0.1% of 2-mercapto ethanol and 0.05% sodium arsenite" by andf when so weight of the nitrogen solution. This substantially reduces the rate of corrosion of the metal equipment by the nitrogen solution arid mamtains the solution veryclear for approximately thirty days. For, at least the next fifteen days these desirable results are still achieved but "to a lesser extent. Although it is not definitelyknown how the nitrogen solution iskept clear inspite of the formation of corrosion products, such as oxides of iron, there is reasonably-strong evidence that the inhibitordissolves these products colorless.

From the example set forth hereinbefore, it will be ,seen that when 2-mercapto'ethanol was used alone its effect in reducing the corrosion was practically the same as conventional inhibitors such as sodium arsenite, ammonium thiocyanate and butyl mercaptan. However, Z-mercapto ethanol used alone was farsuperior' to conventional inhibitors in maintaining the nitrogen solution clear. When 2mercapto ethanol "was combined with sodium arsenite, thisisuperiority in clarity ofthe nitrogen solution again resulted,

and the corrosion-inhibiting power of; the combination was many times better than either of these two compounds/used separately or the sum -of their separate effects-a vast synergistic eftest period of 30 days and the corrosion reported fectf ""Similarcombinations of conventional in 1 rial degree.

dissolved they are substantially a ei-ii ei 1. Theu easonvfor this -=synergism1is*- not known. While it" isnot intended to limit this invention to any tl'ieory by way of'one possible explanation there is some evidence that compounds containing an OH" group andanSI-I group (e.-g.' -2 mercaptoflethanol) react with inorganic trivalent arsenic compounds) (e: g. sodium arsenite) to produceanew-compound, and actually the new compound produces the desired result. This evidence consists of the observation that a large amount of heat is liberated when Z-mercapto ethanol.lisiadded tosodium arsenite, and that, in addition to temperature increase, hydrogen sulfide s-s sliberat d-whe z-ms sc ethanol is added to sodium thioarsenite.

Agm'any apparently widely difierent em-bodi merits: of this invention may be"- made without departing from-the spiritand scope thereof,-it

is l to be 'understood' that the? invention is; not limited to'the specific embodiments thereof except as defined in the appended claims.

What is claimed is:

1. Process of reducing corrosion of a ferrous metal by an ammoniacal solution of a nitrogen compound, which comprises incorporating in said solution a compound having an SH group and an OH group together with an inorganic trivalent arsenic compound, the amounts of said compounds being sufficient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

2. Process of reducing corrosion of a ferrous metal by an ammoniacal' ammonium nitrate solution, which comprises incorporating in said solution a compound having an SH group and an OH group together with an inorganic trivalent arsenic compound, the amounts of said compounds being sufiicient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

3. Process of reducing corrosion of a ferrous metal by an ammoniacal solution of a nitrogen compound, which comprises incorporating in said solution an inorganic trivalent arsenic compound together with a compound selected from the group consisting of 2-mercapto ethanol and 2,3- dimercapto propanol-l, the amounts of said compounds being sufilcient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

4. Process of reducing corrosion of a ferrous metal by an ammoniacal solution of a nitrogen compound, which comprises incorporating in said solution sodium arsenite together with a compound selected from the group consisting of 2-mercapto ethanol and 2,3-dimercapto propa nol-l, the amounts of said compounds being sufficient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

5. Process of reducing corrosion of a ferrous metal by an ammoniacal solution of a nitrogen compound, which comprises incorporating in said solution 0.005%-l% of an inorganic trivalent arsenic compound together with 0.005%- 1% of a compound selected from the group consisting of Z-mercapto ethanol and 2,3-dimercapto propanol-l, the amounts of said compounds being by weight of said solution and sufflcient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

6. Process" of reducing corrosion of atferrous metal b'y 'ajn-ammoniacal amnioniummitr'ate s'olution, which comprises incorporating in said" solution" sodium arsenite and 2-mercapto' ethanol; the amounts of said compounds being sufficient to substantially'reduce the rate of corrosion of a ferrous metal by the-solution, andcontacting said solution withsaid ferrous" metal; 1

7; Process of reducingcorro'sion' of a" ferrous metal by an ammoniacal ammonium lnitratelsolue tion, which comprises incorporating in said so'lution' 0.05 %0.1 of sodium arsenite and: 0.05 0.1% of 2-mercapto ethanol, theamounts of said compounds being by weight' 'of said solution and sufiicient to substantially reduce' the rate of corrosion of a 'ferrous metal by t-he solution and contacting said 1 solution' withi's'aid' 'ferrous :metal; '8. Process 'of reducing corrosion of" a rmus metal by an ammoniacal ammonium. nitrate solution, which comprises incorporating in said solution sodium arsenite" and I 2,3-"dime'rc'a'pto propanol-l, the amounts-of saidcompounds being sufflcient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal. 9. Process of reducing corrosion of a ferrous metal by an ammoniacal ammonium nitrate solution, which comprises incorporating in said solution 0.05%-0.l% of sodium arsenite and 0.05%-0.1% of 2,3-dimercapto propanol-l, the amounts of said compounds being by weight of said solution and sufiicient to substantially reduce the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal. 7

10. A non-corrosive liquid comprising an ammoniacal solution of a nitrogen compound, a compound having an SH group and an OH group and an inorganic trivalent arsenic compound, the amounts of said compounds being sufiicient to substantially reduce the rate of corrosion of a ferrous metal by said solution.

11. A non-corrosive liquid comprising an ammoniacal ammonium nitrate solution, a compound having an SH group and an OH, group and an inorganic trivalent arsenic compound, the amounts of said compounds being sumcient to substantially reduce the rate of corrosion of a ferrous metal by said solution.

12. A non-corrosive liquid comprising an ammoniacal solution of a nitrogen compound, an

inorganic trivalent arsenic, compound, and a compound selected from the group consisting of 2-mercapto ethanol and 2,3-dimercapto propanol-l, the amounts of said compounds being sufficient to substantially reduce the rate of corrosion of a ferrous metal by said solution.

13. A non-corrosive liquid comprising an am 15. A non-corrosive liquid comprising an amy moniacal ammonium nitrate solution, 0.05%-

7 o,1' r sodium arsenite' and o.o5%-o.1% -01 2 -merc apto ethanol, the amounts of said compounds being byweight of said solution and sufiicientpto substantially reduce the rate of corrosion of a ierrous metal pysai d. solution.

16. A non-corrosive liquid comprising an ammoniacal ammonium nitrate solution, 0.05%- 0.1% of sodium, arsenite and; 0.05%- 0.1% of Z-mercapto ethanol, the amounts ofsaid compounds being by weight of said solution and summoniacal ammonium nitrate solution, 0.05

0.1% of sodium arsenite and 0.05%;0.-1% o!- 2,3-dimercapto propanol-i, the amounts of said compounds being by weightof said solution andsufficient to substantially reducethe rate of cor rosion of a ferrous metal by said solution.

MARION D. BARNES. BOYD L. EMBREY.

RUSSELL E. Koo'Ns;

REFERENCES CITED The following references areoi record in the;

file of this patent: V. UNITED STATES PATENTS, g

. Date Number Name l v 2,198,151 Beekhuis et a1. Apr. 23, 1940- 2,215,077 Beekhuis et a1. Sept. 17,1940 2,215,092 Beekhuis et a1 Sept. ,17, 1940* 2,220,059 Beekhuis et al. Nov. 5, 1940 2,238,651

Keenen Apr. 15, 194i 

1. PROCESS OF REDUCING CORROSION OF A FERROUS METAL BY AN AMMONIACAL SOLUTION OF A NITROGEN COMPOUND, WHICH COMPRISES INCORPORATING IN SAID SOLUTION A COMPOUND HAVING AN SH GROUP AND AN OH GROUP TOGETHER WITH AN INORGANIC TRIVALENT ARSENIC COMPOUND, THE AMOUNTS OF SAID COMPOUNDS BEING SUFFICIENT TO SUBSTANTIALLY REDUCE THE RATE OF CORROSION OF A FERROUS METAL BY THE SOLUTION, AND CONTACTING SAID SOLUTION WITH SAID FERROUS METAL. 